A VARIETY of clues to the motives of Dylann Storm Roof, the suspect in last week’s mass shooting at Emanuel African Methodist Episcopal Church in Charleston, S.C., have emerged. First, we saw the patches he wore on his jacket in a Facebook photo: the flags of regimes in South Africa and Rhodesia that brutally enforced white minority rule.

Then, a further cache of photos of Mr. Roof — seen in several bearing a Confederate flag — was discovered on a website, Last Rhodesian, registered in his name, together with a manifesto, a hodgepodge of white supremacist ideas. The author (most likely Mr. Roof) calls on whites to take “drastic action” to regain dominance in America and Europe.

These themes, popular among white supremacists in the United States, are also signs of the growing globalization of white nationalism. When we think of the Islamist terrorism of groups like Al Qaeda and the Islamic State, we recognize their international dimension. When it comes to far-right domestic terrorism, we don’t.

Americans tend to view attacks like the mass murder in Charleston as isolated hate crimes, the work of a deranged racist or group of zealots lashing out in anger, unconnected to a broader movement.